An electric vehicle uses electrical energy as a main energy source, unlike an internal-combustion engine vehicle using fossil fuel as a main energy source. Accordingly, the electric vehicle essentially needs a high-voltage battery to store electrical energy, a motor as a power source, and an inverter to drive the motor. In order to increase a driving distance and efficiency of power consumption of the electric vehicle, use of a large-capacity battery is increasing. Further, efforts for increasing the efficiency of the inverter and the motor are actively conducted.
One of methods for improving the efficiency of the inverter and the motor is to raise a battery voltage. For example, doubling a battery voltage can reduce current flowing to the inverter and the motor to ½ to obtain the same output power since P=VI, and can reduce conduction loss (I2R) to ¼. Accordingly, the efficiency of the inverter and the motor can increase by the amount of reduction of the conduction loss. If a power element and a conductor having high conduction resistance are used, the sizes of connection connectors connecting the battery, the inverter, and the motor, as well as the sizes of the inverter and the motor can be reduced, which leads to a reduction of cost.
However, increasing a battery voltage has one limitation. Most of commercialized rapid chargers charge batteries having a charging voltage of about 200V to 500V. Accordingly, a battery having a high charging voltage of 800V or more for high efficiency cannot be charged by typical rapid chargers that charge batteries having a charging voltage of 200V to 500V. That is, compatibility with the typical rapid chargers acts as a limiting factor in raising the battery voltage of the electric vehicle. For this reason, a rapid charger capable of outputting (charging) a high voltage should be developed and installed in order to raise the battery voltage of the electric vehicle.